Siemens Drive | Fault Code 7902
Fault Code 7902 typically corresponds to:
"PROFIBUS: Cyclic connection failed" (or PROFINET equivalent, depending on the telegram type)
In SINAMICS firmware versions (e.g., V4.7+), 7902 indicates that the master-slave cyclic communication has been interrupted or never established. The drive is configured for fieldbus control (e.g., P0700 = 6 for PROFIBUS, or P0922 telegram selected) but no valid cyclic data exchange is occurring.
Disconnect drive terminals and measure resistance at room temperature. Should be ~600Ω. Use a hairdryer to warm probe—resistance should increase smoothly.
Before diving into causes, it helps to recognize how this fault manifests:
The Siemens drive fault code F7902 (or 7902) Motor Stalled (or "Motor out of step"). This fault occurs when the drive detects that the motor is not rotating despite a torque or current being applied, or it has lost synchronism with the drive's output frequency. Common Causes Mechanical Overload:
The load is too heavy for the motor to start or maintain rotation, causing it to stall. Incorrect Motor Data:
The drive's parameters do not match the actual motor (e.g., rated current, power factor, or resistance). Incomplete Identification: siemens drive fault code 7902
A "Motor Data Identification" (MotID) or static optimization run was not completed correctly during commissioning. Ramp Settings: The acceleration ramp ( cap P 1120
) is too short, or the torque limits are set too low to overcome initial friction. Phase Failure:
A loose connection or broken cable between the drive and the motor. Troubleshooting & Solutions Check for Mechanical Obstructions:
Manually rotate the motor (if safe) to ensure the load isn't seized or jammed. Verify Parameter Settings:
Cross-check the motor nameplate against the drive parameters ( Perform Motor ID: Re-run the motor data identification (
or similar, depending on the model) to allow the drive to "learn" the motor's electrical characteristics. Increase Current/Torque Limits: Check if the stall detection limits ( cap P 2175 cap P 2177 ) are too sensitive for your specific application. Extend Ramp Times: Fault Code 7902 typically corresponds to: "PROFIBUS: Cyclic
Increase the acceleration time to give the motor more time to reach speed without hitting the stall threshold. If you are using a SINAMICS G120XA
, this fault is frequently tied to asynchronous motors that haven't undergone proper static optimization. You can view the specific fault history and timestamps using the Siemens STARTER software TIA Portal specific parameter numbers for a particular Siemens drive series, like the
Subject: G120XA solution to warning F7902 motor out of step - Siemens
Understanding and Resolving Siemens Drive Fault Code 7902 The Siemens Drive Fault Code 7902 (often displayed as F07902) is a critical error indicating a "Motor Stalled" condition. This fault occurs when the drive’s control logic determines that the motor is not rotating as expected despite receiving power, or when the deviation between the calculated motor speed and the actual measured speed exceeds defined limits.
While this fault is common across various series including SINAMICS S120, G120, G120XA, and G115D, its root causes can range from simple mechanical blockages to complex parameterization errors. Primary Causes of Fault 7902
Understanding why the drive triggers a stall fault is the first step in troubleshooting. Common triggers include: SINAMICS G120XA fault F07902 - ID: 109773411 - Support Before diving into causes, it helps to recognize
This is a diagnostic and troubleshooting report for Siemens Drive Fault Code 7902.
| Drive Family | Fault Code | Notes | |--------------|------------|-------| | Sinamics S120 | F07902 | Also logs additional info in r0949 (phase affected: 1=U, 2=V, 3=W) | | Sinamics G120 (CU240E) | F07902 | Can be temporarily inhibited via p2118/p2119 (not recommended for permanent fix) | | Masterdrives (6SE70) | F023 or F024 (older codes) | 7902 appears as “Phase failure output” in newer software versions | | Simotion / Sinamics S150 | F7902 | Same root cause; check also motor holding brake wiring |
Siemens drives do not rely solely on external sensors. They use internal current measurement at the inverter’s output stage. When the motor is running, the drive expects balanced currents. If one phase deviates by more than a programmable tolerance (typically set via parameter p3230 in Sinamics), the drive triggers fault 7902.
This fault is usually latched—meaning the drive will not restart automatically. It requires a manual reset after the root cause is fixed.
Open circuit → infinite ohms → fault 7902.
Short circuit → near 0Ω → fault 7902.